1. Field of the Invention
This invention relates to deformable mirrors in general, and in particular to deformable mirrors having electrically operated actuators used for deforming the mirror's reflecting surface.
2. Summary of the Prior Art
It is well known in the prior art to use deformable mirrors to correct optical signals for aberrations introduced into a wavefront due to the transmission of an optical signal through a distorting medium, e.g. the earth's atmosphere. Such deformable mirrors may be used, for example, to correct aberrations introduced into laser signals or optical images imaged by a telescope as they pass through the earth's atmosphere, or to introduce known aberrations into a laser signal prior to its transmission through the earth's atmosphere. Examples of deformable mirrors which may be used to perform the foregoing function appear in U.S. Pat. Nos. 3,904,274 and 4,657,358 which are owned by the assignee of the present invention and the teachings of which are incorporated herein by reference. Mirror's of the foregoing type employ a plurality of actuators, for example piezoelectric actuators, which are independently operable to selectively deform areas of a deformable reflecting surface to correct known anomalies contained in an impinging optical signal's wavefront. Signals for driving the actuators to correct the aberrated wavefront may be provided by a wavefront sensing and correction system such as that described in U.S. Pat. No. 3,923,400, the teachings of which are also incorporated herein by reference.
The use of wavefront control systems, for example deformable mirrors, in large aperture optical systems mandates the use of a large diameter mirror to achieve effective wavefront control. Additionally, such a system should ideally also contain a large number of closely spaced actuators to permit adjustments to be made at locations closely spaced together across the deformable mirror's reflecting surface. To accommodate the foregoing requirements, a deformable mirror will frequently require the use of a large number of actuators to achieve effective control of the mirror's reflecting surface.
As noted in U.S. Pat. No. 4,657,358, actuators for use in controlling a deformable mirror may be manufactured from stacks of electrodistortive material, for example lead magnesium niobate (PMN) or lead zirconate titanate (PZT). The electrodistortive material is interleaved in the stack with alternating layers of electrical conductors to permit the application of an electrical signal to the material.
Prior known deformable mirrors which utilize stacked electrodistortive material to provide control of the mirror's reflecting surface have been constructed with the actuators rigidly fastened to the structure supporting the mirror's reflecting surface, for example by cement or a frit bond. Such construction has not provided for the ease of repair of a deformable mirror in the event of a failure of one or more actuators. In the event of the failure of an actuator due, for example, to the mechanical failure of an actuator or to the failure of electrical contacts between one or more layers of electrodistortive material, the components of the mirror had to be carefully disassembled to effect the removal and replacement or repair of the failed actuator. Such a disassembly procedure is time consuming, frequently difficult and often impossible to effect due to the spacing between adjacent actuators and the need to prevent damaging good actuators during the repair procedure. Consequently, there is a need for a deformable mirror which utilizes electrically operated actuators which may be easily replaced without damaging other actuators during the replacement procedure. A related requirement is for a deformable mirror having replaceable actuators which may be easily adjusted during the replacement procedure to control their influence on the deformation of a deformable mirror's reflecting surface.